1. Field of the Invention
The present invention relates to an ophthalmic image taking apparatus having an image taking optical system for imaging an image on an image sensing element at different imaging magnifications and an ophthalmic image taking method.
2. Related Background Art
A nondissipative pupil fundus camera for recording data in various image taking media has been known so far. The nondissipative pupil fundus camera observes and aligns a person to be examined under a natural dissipative pupil state by infrared light to record the static image of a color fundus image by visible flash generated by a stroboscope light source. Therefore, when image taking light dazzles, the pupil of the person to be examined contracts. Therefore, when continuing image taking, it is necessary to wait for approx. 10 min until the pupil becomes the natural dissipative pupil.
In the case of fundus image taking of mass survey, it is requested to image-take right and left eyes of many persons. Therefore, it is temporally spatially low efficient to make a person to be examined wait until the other eye is image-taken after completing image-taking of either eye. Therefore, image taking at a low light intensity is requested so that right and left eyes can be continuously image-taken.
In recent years, the number of methods for respectively recording a fundus image by using an electronic recording camera has been increased. However, when performing image-taking at a less illumination light intensity by using the camera, the image-taking sensitivity of the camera is raised.
Moreover, images of mass survey are frequently image-taken by an image-taking person. However, to shorten the image-taking time, a method for transferring an image to a distant place by using a network line is used. However, when an image size is large, transfer requires a lot of time and the image-taking efficiency is lowered. Therefore, as disclosed in Japanese Patent Application Laid-Open No. H06-098859, a method for decreasing the capacity of image information by using an image compression technique is used. Moreover, Japanese Patent Application Laid-Open No. H04-084932 discloses a technique for cutting out and transferring only a fundus image portion.
However, in the case of the above conventional method, not only a fundus image set by raising the image-taking sensitivity but also noises such as dark current are amplified. Moreover, to decrease an image size by using a compression technique, it is necessary to use irreversible compression. Therefore, a peculiar pattern appears on an image or color information is lost.
In the case of a medical image, a raw image (raw data) which is not worked is requested and an compressed image may not be recognized as a diagnostic image. When taking out only a fundus image, the shape of the image becomes a specific shape such as a circle or ellipsoid and it cannot be correctly reproduced by general viewer software. Moreover, because the image is imaged in a small shape, it is necessary to enlarge and display the image when displaying it on a monitor in order to remove an increased margin.